Recombinant Trichodesmium erythraeum Photosystem Q (B) protein 1 (psbA1)
Description
Molecular Overview
psbA1 encodes the D1 protein, a core component of PSII responsible for water splitting and oxygen evolution . The recombinant form is expressed in E. coli with a His-tag for purification, retaining full-length functionality (1-344 amino acids) . Key specifications include:
Functional Role in Photosynthesis
psbA1 enables PSII’s Q<sub>B</sub> site to accept electrons from Q<sub>A</sub>, driving plastoquinone reduction and proton translocation . Under iron deficiency, Trichodesmium upregulates isiA (a homolog of CP43) and modifies PSII activity, highlighting psbA1’s adaptability to environmental stress .
Expression Under Stress
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Iron Limitation: Trichodesmium consortia under Fe-depleted conditions show altered chlorophyll fluorescence profiles (peak shift from 680 nm to 675 nm) and increased isiA expression, correlating with PSII remodeling .
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Transcriptional Regulation: Low-oxygen conditions induce psbA1 in cyanobacteria like Synechocystis sp. PCC 6803, suggesting conserved stress-response mechanisms .
Metatranscriptomic Insights
Treatment with Synechococcus filtrate downregulated Trichodesmium genes for Fe uptake (tonB, exbB), photosynthesis (psaA), and nitrogen fixation, indicating interspecies competition impacting psbA1-associated pathways .
Applications
Product Specs
Note: While we prioritize shipping the format currently in stock, we can accommodate specific format requests. Please indicate your preferred format during order placement, and we will fulfill your requirement.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please communicate with us in advance, as additional fees will apply.
Generally, liquid formulations have a shelf life of 6 months at -20°C/-80°C. Lyophilized forms typically have a shelf life of 12 months at -20°C/-80°C.
Target Background
KEGG: ter:Tery_0182
STRING: 203124.Tery_0183
Q&A
Basic Research Questions
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What is the function of psbA1 in Trichodesmium erythraeum?
The psbA1 gene in Trichodesmium erythraeum encodes the D1 protein, a core component of Photosystem II (PSII). This protein is integral to the photosynthetic electron transport chain and functions at the QB binding site where plastoquinone reduction occurs during photosynthesis. The D1 protein is particularly significant in Trichodesmium due to the organism's unique temporal segregation of photosynthesis and nitrogen fixation processes.
Studies of Trichodesmium erythraeum IMS101 have shown that photosynthetic electron transport rates (rPm) are highly responsive to environmental conditions, suggesting that the D1 protein encoded by psbA1 plays a critical role in adapting photosynthetic capacity to changing environments . The protein undergoes rapid turnover, especially under high light conditions, which is essential for maintaining photosynthetic efficiency in the marine environments where Trichodesmium thrives.
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How does the expression of psbA1 relate to the temporal segregation of photosynthesis and nitrogen fixation?
Trichodesmium erythraeum exhibits a remarkable temporal separation between photosynthesis and nitrogen fixation activities, which can be observed under various day-night cycles. This separation is influenced by light exposure duration and intensity.
Research has demonstrated that under 12L:12D, 8L:16D, and 16L:8D light-dark cycles, Trichodesmium consistently shows a time lag between peak nitrogen fixation and minimum carbon fixation . The psbA1 gene expression follows specific patterns that support this segregation, with expression levels typically higher during periods of active photosynthesis. This temporal regulation helps protect the oxygen-sensitive nitrogenase enzyme from the oxygen produced during photosynthesis.
Experimental data indicates that elongating the light period leads to higher nitrogen fixation rates under low light conditions compared to high light, while shortening light exposure to 8 hours delays nitrogen fixation peak time to the end of the light period and extends it into the night . These observations suggest that psbA1 expression must be precisely coordinated with these physiological shifts.
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How do environmental factors affect psbA1 expression in Trichodesmium erythraeum?
The expression of psbA1 in Trichodesmium erythraeum is significantly influenced by multiple environmental factors, particularly iron availability, CO2 concentration, and light intensity.
| Environmental Factor | Effect on psbA1 Expression | Physiological Impact |
|---|---|---|
| Iron Limitation | Generally decreased | Reduced photosynthetic capacity |
| High CO2 (720 μatm) | Enhanced | Increased growth rates and photosynthetic efficiency |
| High Light (400 μmol photons m-2 s-1) | Upregulated | Higher relative PSII electron transport rates |
| Low Light (40 μmol photons m-2 s-1) | Downregulated | Lower photosynthetic capacity but more efficient resource allocation |
Under iron-limiting conditions, Trichodesmium shows adaptation strategies that include modified resource allocation to photosynthetic proteins, with high light conditions potentially leading to increased growth rates despite iron limitation . Higher CO2 concentrations have been shown to increase growth rates across all iron concentrations and enable growth at lower Fe' concentrations, suggesting complex interactions between carbon availability and psbA1 function .
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What methodologies are used to express recombinant psbA1 protein from Trichodesmium erythraeum?
Expression of recombinant psbA1 protein from Trichodesmium erythraeum typically employs heterologous expression systems. The challenges include the membrane-bound nature of the D1 protein and maintaining its functional integrity.
Common expression methodologies include:
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E. coli-based expression systems: Using vectors with inducible promoters, though optimization is required due to the membrane-associated nature of the D1 protein.
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Cyanobacterial hosts: Expression in model organisms like Synechocystis PCC 6803 provides a more native-like environment for proper folding and membrane integration.
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Heterologous gene expression approach: Similar to the method used for studying Trichodesmium phosphite dehydrogenase, where researchers expressed Trichodesmium genes in Synechocystis PCC 6803 to confirm function when direct genetic manipulation was challenging .
Purification typically involves membrane solubilization using detergents, followed by affinity chromatography using epitope tags. Verification of functionality can be performed through reconstitution experiments or complementation studies in D1-deficient mutants.
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What is known about the genomic context of psbA1 in Trichodesmium erythraeum?
The genomic context of psbA1 in Trichodesmium erythraeum IMS101 is particularly interesting due to the organism's unusual genome structure. Unlike most free-living cyanobacteria, only 63.8% of the T. erythraeum genome is predicted to encode proteins, which is 20-25% less than the average for other cyanobacteria .
The psbA1 gene exists within this genome with extensive non-coding regions. Transcriptomic analysis indicates that 86% of these non-coding spaces are expressed, suggesting potential regulatory functions . The conservation of intergenic regions across spatiotemporally separated Trichodesmium populations indicates possible genus-wide selection for their maintenance.
This genomic architecture likely influences the regulation and expression of photosynthetic genes including psbA1. The gene may be subject to complex regulation involving both coding and non-coding elements, contributing to the unique physiological capabilities of Trichodesmium in balancing photosynthesis with nitrogen fixation.
Advanced Research Questions
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How do mutations in psbA1 affect the photosynthetic efficiency and nitrogen fixation capacity in Trichodesmium erythraeum?
Mutations in the psbA1 gene can significantly impact both photosynthetic efficiency and nitrogen fixation in Trichodesmium erythraeum due to the interdependence of these processes. Research suggests that mutations affecting the QB binding pocket can disrupt electron transport kinetics, which in turn affects oxygen evolution patterns critical for protecting nitrogenase activity.
The effects of psbA1 mutations can be categorized as follows:
| Mutation Target | Effect on Photosynthesis | Effect on N2 Fixation | Experimental Approach |
|---|---|---|---|
| QB binding pocket | Altered electron transport kinetics | Disrupted temporal segregation | Site-directed mutagenesis, O2 evolution measurement |
| D1 turnover domains | Changed repair cycle efficiency | Modified diel rhythm | Pulse-chase labeling, nitrogenase activity assays |
| Regulatory regions | Altered expression patterns | Impact on diurnal separation | Reporter gene fusions, RT-qPCR |
While direct genetic manipulation of Trichodesmium remains challenging, approaches similar to those used for studying phosphite utilization genes could be adapted. Researchers have successfully demonstrated function by expressing Trichodesmium genes in model cyanobacteria like Synechocystis PCC 6803 .
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What techniques are most effective for studying the interaction between psbA1 and nitrogen regulatory pathways in Trichodesmium erythraeum?
Studying the interaction between psbA1 and nitrogen regulatory pathways in Trichodesmium erythraeum requires sophisticated methodological approaches that can capture the dynamic relationship between photosynthesis and nitrogen fixation.
Effective techniques include:
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Transcriptomic analysis: RNA-seq experiments capturing the temporal expression patterns of psbA1 alongside nitrogen regulatory genes like ntcA, napA, and nifH can reveal coordinated expression patterns.
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Protein-protein interaction studies: Co-immunoprecipitation followed by mass spectrometry to identify interactions between D1 protein and components of nitrogen regulatory networks.
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Chromatin immunoprecipitation (ChIP): To identify potential transcription factors binding to the psbA1 promoter under different nitrogen conditions.
Research has shown that the regulation of nitrogen metabolism in Trichodesmium is uniquely decoupled from typical cyanobacterial patterns. For instance, the ntcA gene (a nitrogen regulatory gene) transcription remains high even in the presence of ammonium, contrary to patterns observed in other cyanobacteria . This suggests that studying psbA1 regulation must account for these unique regulatory mechanisms in Trichodesmium.
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How does the psbA1 product function under iron limitation conditions in Trichodesmium erythraeum?
Iron limitation significantly affects photosynthetic function in Trichodesmium erythraeum, with direct implications for the psbA1 gene product. Under iron-limiting conditions, Trichodesmium exhibits specific adaptations in the photosynthetic apparatus to maintain function while minimizing iron requirements.
Experimental data shows that:
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Iron limitation decreases the maximum relative PSII electron transport rates (rPm), directly impacting the function of the D1 protein encoded by psbA1 .
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Under iron limitation, high light conditions can actually increase growth rates and rPm, suggesting a complex interaction between light energy and iron availability .
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Higher CO2 concentrations can partially compensate for iron limitation effects on photosynthesis, reducing the iron half-saturation constants for growth (Km) .
These observations indicate that the psbA1 product likely undergoes structural or functional modifications under iron limitation, possibly including altered turnover rates or post-translational modifications to optimize performance with limited iron cofactors.
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What bioinformatic approaches are most valuable for analyzing psbA1 sequence conservation across Trichodesmium populations?
Analyzing psbA1 sequence conservation across Trichodesmium populations requires specialized bioinformatic approaches that can account for the unique genomic features of this organism.
Recommended bioinformatic approaches include:
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Comparative genomics: Analysis of psbA1 sequences from diverse Trichodesmium populations to identify conserved domains versus variable regions.
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Structural prediction: Modeling the impact of sequence variations on protein structure and function, particularly in relation to the QB binding pocket.
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Selection pressure analysis: Identifying signatures of purifying or diversifying selection across different domains of the psbA1 gene.
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How can transcriptomic data be leveraged to understand psbA1 regulation in the context of Trichodesmium's unusual genome architecture?
Trichodesmium erythraeum possesses an unusual genome with extensive non-coding regions, many of which are transcribed. Leveraging transcriptomic data to understand psbA1 regulation requires specialized approaches that account for this unique genomic architecture.
Effective strategies include:
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Strand-specific RNA sequencing: To identify antisense transcripts and non-coding RNAs that may regulate psbA1 expression.
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Differential expression analysis: Comparing psbA1 expression patterns under varying environmental conditions alongside changes in non-coding RNA expression.
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RNA structurome analysis: Identifying conserved RNA secondary structures in non-coding regions that might influence psbA1 expression.
Research has shown that Trichodesmium has "the highest number of actively splicing group II introns and the highest percentage of TSS yielding ncRNAs of any bacterium examined to date" . These elements likely play important roles in regulating gene expression, including photosynthetic genes like psbA1. Additionally, transcriptomic data reveals that 86% of the non-coding space is expressed, though the function of these transcripts remains largely unclear .
Methodological Research Questions
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What protocols can be used to study the diel rhythm of psbA1 expression in relation to nitrogen fixation in Trichodesmium?
Studying the diel rhythm of psbA1 expression in relation to nitrogen fixation requires carefully designed experimental protocols that can capture the temporal dynamics of these processes.
Recommended protocols include:
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Synchronized culture establishment: Using light/dark cycles (12L:12D, 8L:16D, or 16L:8D) to establish consistent biological rhythms in Trichodesmium cultures .
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Time-course sampling: Collecting samples at regular intervals (typically every 2-4 hours) across a complete diel cycle.
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Multiplex analysis: Simultaneously measuring:
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psbA1 transcript levels via RT-qPCR
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D1 protein abundance via immunoblotting
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Photosynthetic activity via pulse amplitude modulated (PAM) fluorometry
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Nitrogen fixation rates via acetylene reduction assays
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Research has shown that under different light-dark cycles, Trichodesmium consistently exhibits temporal segregation between photosynthesis and nitrogen fixation, with specific patterns depending on light dose . For instance, elongating the light period leads to higher nitrogen fixation rates under low light conditions, while shortening light exposure delays the nitrogen fixation peak .
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How can researchers effectively measure the impact of CO2 concentration on psbA1 function in Trichodesmium erythraeum?
Measuring the impact of CO2 concentration on psbA1 function in Trichodesmium erythraeum requires multifaceted experimental approaches that assess both molecular and physiological parameters.
Effective experimental design should include:
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Controlled CO2 conditions: Establishing cultures under different CO2 concentrations (e.g., 180, 380, and 720 μatm) using bubbling systems or pH-stat approaches .
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Combined factor experiments: Testing CO2 effects alongside other variables like iron concentration and light intensity to capture interaction effects .
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Comprehensive measurements:
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Growth rates under different CO2 and iron conditions
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Photosynthetic electron transport rates using PAM fluorometry
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psbA1 transcript abundance via RT-qPCR
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D1 protein turnover rates using pulse-chase labeling
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Research has demonstrated that higher CO2 (720 μatm) increases growth rates across all iron concentrations, enables growth at lower Fe' concentrations, increases relative PSII electron transport rates (rPm), and lowers the iron half-saturation constants for growth (Km) . These findings suggest complex interactions between carbon availability and photosynthetic function that directly involve the psbA1 gene product.
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What approaches can be used to study post-translational modifications of the psbA1 gene product in Trichodesmium?
The D1 protein encoded by psbA1 undergoes various post-translational modifications (PTMs) that are critical for its function and turnover. Studying these modifications requires specialized proteomic approaches.
Recommended methodologies include:
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Targeted mass spectrometry: Using multiple reaction monitoring (MRM) to detect specific phosphorylation, oxidation, or other modification events on the D1 protein.
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PTM enrichment techniques: Employing phosphopeptide enrichment using TiO2 or immunoprecipitation with modification-specific antibodies prior to analysis.
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Comparative PTM mapping: Analyzing D1 protein modifications under different environmental conditions (light intensity, iron availability, nitrogen source) to identify condition-specific patterns.
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Site-directed mutagenesis: Creating targeted mutations at putative modification sites to assess functional impacts.
Understanding these modifications is particularly relevant given Trichodesmium's complex photosynthetic regulation. The temporal segregation of photosynthesis and nitrogen fixation observed under various day-night cycles likely involves coordinated post-translational regulation of key photosynthetic proteins, including the D1 protein.
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How can heterologous expression systems be optimized for functional studies of Trichodesmium erythraeum psbA1?
Optimizing heterologous expression systems for functional studies of Trichodesmium erythraeum psbA1 requires addressing several technical challenges related to membrane protein expression and functional assessment.
Key optimization strategies include:
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Host selection: Utilizing cyanobacterial hosts like Synechocystis PCC 6803 that provide a more native-like environment for proper folding and cofactor insertion .
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Expression vector design: Implementing inducible promoters with fine-tuned expression control to prevent toxicity from membrane protein overexpression.
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Affinity tag placement: Strategically positioning tags to minimize interference with protein function while enabling purification.
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Functional verification: Employing complementation assays in D1-deficient mutants to confirm activity.
This approach has been successfully demonstrated for other Trichodesmium proteins, such as the phosphite utilization genes (ptxABCD). Researchers expressed these genes in Synechocystis PCC 6803 and demonstrated that combined expression of both the transporter and dehydrogenase enabled phosphite utilization . Similar approaches could be applied to study psbA1 function.
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What methodologies are effective for analyzing the relationship between nitrogen source availability and psbA1 expression in Trichodesmium?
The relationship between nitrogen source availability and psbA1 expression in Trichodesmium erythraeum is complex and requires specialized methodological approaches to elucidate.
Effective methodologies include:
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Controlled nitrogen source experiments: Growing cultures with different nitrogen sources (N2, NH4+, NO3-, NO2-, urea) at varying concentrations .
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Gene expression analysis: Quantifying psbA1 transcript levels alongside nitrogen regulatory genes (ntcA, napA, nifH) using RT-qPCR under different nitrogen conditions .
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Physiological measurements: Simultaneously assessing growth rates, photosynthetic parameters, and nitrogen assimilation rates to correlate with gene expression data.
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Inhibitor studies: Using inhibitors like L-methionin-DL-sulfoximine (MSX, a glutamine synthetase inhibitor) to manipulate internal nitrogen status and observe effects on psbA1 expression .
Research has shown that Trichodesmium exhibits unique responses to different nitrogen sources. While ecologically relevant nitrogen concentrations (2-20 μM) suppress growth and assimilation, much higher concentrations are required to affect transcript levels of nitrogen-related genes . Additionally, nitrogen regulation in Trichodesmium shows unusual features, such as high ntcA transcript levels even in the presence of ammonium . These unique regulatory patterns likely extend to photosynthetic genes like psbA1.
